Vibrational circular dichroism of methylthiirane (original) (raw)
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The Journal of Physical Chemistry A
Vibrational circular dichroism (VCD) spectra and the corresponding IR spectra of the chiral isomers of methyloxirane and of methylthiirane have been reinvestigated, both experimentally and theoretically, with particular attention to accounting for anharmonic corrections, as calculated by the GVPT2 approach. De novo recorded VCD spectra in the near IR (NIR) range regarding CH-stretching overtone transitions, together with the corresponding NIR absorption spectra, were also considered and accounted for, both with the GVPT2 and with the local mode approaches. Comparison of the two methods has permitted us to better describe the nature of active "anharmonic" modes in the two molecules and the role of mechanical and electrical anharmonicity in determining the intensities of VCD and IR/NIR data. Finally, two nonstandard IR/NIR regions have been investigated: the first one about ≈2000 cm −1 , involving mostly two-quanta bending mode transitions, the second one between 7000 and 7500 cm −1 involving three-quanta transitions containing CH-stretching overtones and HCC/HCH bending modes.
Journal of the American Chemical Society, 1987
The CH stretching Raman, FTIR, and vibrational circular dichroism (VCD) spectra of 3(R)-methylcyclohexanone and its chiral 2,2,6,6-d,, 4,4-d2, 5,5-d2 and methyl-d, isotopomers, and the Raman and FTIR spectra of racemic 3-methylcyclohexanone-3-dl are presented and analyzed. Fourier self-deconvolution has been applied to the F U R spectra to artificially enhance the resolution in order to determine individual band frequencies. Band assignments have been obtained on the basis of the spectral changes occurring due to selective deuteriation and from an analysis of the strong Fermi resonance interactions. The VCD spectral features of the five chiral isotopomers can all be understood in terms of the coupling of pairs of chirally oriented CH oscillators on adjacent carbon atoms and the removal of the degeneracy in the methyl modes.
Molecular orbital approaches to the calculation of vibrational circular dichroism
The Journal of Physical Chemistry, 1984
A new molecular orbital description of vibrational circular dichroism (VCD), the nonlocalized molecular orbital model (NMO), is developed. In the CNDO approximation, the NMO-VCD intensity is expressed in terms of one-center charge and rehybridization contributions and two-center current contributions. The NMO model, which is the molecular orbital analogue of previous charge-flow models, is compared to the other molecular orbital approaches to VCD, the localized molecular orbital model (LMO), and the atomic polar tensor model (APT). The APT expressions are shown to arise directly as an approximate form of the NMO expressions. Calculations of the CH-stretching VCD in L-alanine are presented for the three molecular orbital approaches.
Journal of Organic Chemistry, 2001
We report the determination of the absolute configuration (AC) of the chiral sulfoxide, 1-(2methylnaphthyl) methyl sulfoxide, 1, using vibrational circular dichroism (VCD) spectroscopy. The VCD of 1 has been measured in the mid-IR spectral region in CCl 4 solution. Analysis employs the ab initio DFT/GIAO methodology. DFT calculations predict two stable conformations of 1, E and Z, Z being lower in energy than E by <1 kcal/mol. In both conformations the SO bond is rotated from coplanarity with the naphthyl moiety by 30-40°. The predicted unpolarized absorption ("IR") spectrum of the equilibrium mixture of the two conformations permits assignment of the experimental IR spectrum in the mid-IR spectral region. The presence of both E and Z conformations is clearly evident. The VCD spectrum predicted for S-1 is in excellent agreement with the experimental spectrum of (-)-1, unambiguously defining the AC of 1 as R(+)/S(-).
1990
Vibrational rotational strengths are calculated for allene-1,3-d2 by using the fixed partial charge (FPC), localized molecular orbital (LMO), and atomic polar tensor (APT) models and the a priori theory of Stephens. The LMO model is implemented using semiempirical methods. The APT model and the a priori theory are implemented at the ab initio SCF level of approximation. Dipole strengths for allene-1,3-d2, -do, and -d4 are simultaneously calculated. Dipole strengths predicted a priori are in reasonably good agreement with experimental values; the LMO and FPC models give similar and very different results, respectively. Rotational strengths calculated from the FPC, LMO, and APT models overall bear little resemblance to those calculated from the a priori theory.
The theory of vibrational circular dichroism: trans-1,2-dideuteriocyclobutane and propylene oxide
Chemical Physics Letters, 1986
A rigorous theory of vibrational rotational strengths was recently developed by Stephens. We report the first comparisons of calculations using this theory with experimental vibrational circular dichroism data. The theory is implemented using SCF MO electronic wavefunctions and a 4-31G basis set. The molecules studied are tr~s-1,2-dideute~~y~lobutane and propylene oxide. Encouraging agreement between theory and experiment is obtained.
Ational Heterogeneity in and with Vibrational Circular Dichroism Spectroscopy †
2019
Van't Hoff Institute for Molecular Sciences 904, 1098 XH Amsterdam, The Netherlands Deutsches Elektronen-Synchrotron DESY, N Amsterdam Center for Multiscale Modeling, Sciences, Vrije Universiteit Amsterdam, De B Netherlands Radboud University, Institute for Molec Toernooiveld 7c, 6525 ED Nijmegen, The Ne Department of Environmental Science, Phys Blaga University of Sibiu, loan Ratiu Street N p.nicu@gmail.com † Electronic supplementary information used genetic algorithm and cross-valid processed spectra and additional table different levels of theory. See DOI: 10.103 Cite this: DOI: 10.1039/c9sc02866h
Monatshefte f�r Chemie - Chemical Monthly, 2005
A set of vibrational circular dichroism (VCD) spectra in the CH-stretching fundamental region for about twenty compounds belonging to the class of essential oils was empirically analyzed by the use of a sort of vibrational exciton mechanism, involving three centers. Through a general formula applicable to many coupled dipole oscillators, the rotational strengths of the previously identified vibrational excitons are evaluated. The results are then critically reviewed by the use of recent ab initio methodology, as applied to selected molecules of the original set. Further insight is gained by model calculations adding up the contribution of the coupling between electric dipole moments associated with normal mode behavior and that of the polarizability from polarizable groups. The former part is responsible for the excitonic behavior of the VCD spectra. For the same selected molecules we have also investigated whether some excitonic behavior is taking place in the second overtone region, and have concluded that this is not the case.